To quantify the levitation force of HTS samples in the presence of an external magnetic field, a measurement process has evolved. This process, shown in FIG. 1 labeled Previous Testing Method, involves zero-field-cooling a sample 10 in a dish containing a liquid cryogen, such as nitrogen, then moving a reference magnet 12 towards the sample 10 and measuring the repulsive force exerted on the magnet at precise distances from the sample. The force is measured using a load cell 13; the distance is measured and changed using a motion controller system and stage 15. In general, a force vs. separation distance hysteresis curve is generated by use of a well known program entitled "Labview" put out by National Instruments of Austin, Tex., and the curve is extrapolated to a distance of zero. The force at zero distance is termed F.sub.o, and this number is representative of the levitation quality of a given HTS sample.
This measurement heretofore has been performed on one sample at a time. Prior to the subject invention each sample was cemented upright in a Styrofoam dish and cooled with liquid nitrogen. The load cell/magnet probe approached the sample from above to acquire the necessary data. Lengthy set-up times, manual control of liquid nitrogen addition, and cool-down time for each HTS sample ready to be tested made the process slow to produce results, repetitive to perform, and ultimately inaccurate due to human error.
When more samples began accumulating for use such as in an FES (flywheel energy storage) facility, an improved testing method was needed. Preferably, the new method would use the same measurement principles and generate the same curves, but do so more efficiently and accurately.
The machine of the present invention was designed to be loaded with a plurality of samples, each sample preferably being a hexagonally shaped disc, and to provide one hysteresis curve and F.sub.o value for each sample, as quickly and accurately as possible. Because of cost and accuracy considerations, only one load cell/magnet probe was used although more are possible, and the samples were to be tested seriatim.
Accordingly, it is an object of the present invention to provide a machine for determining hysteresis curves and F.sub.o values for HTS samples more rapidly than heretofore possible.
Another object of the invention is to provide a machine for determining hysteresis curves and F.sub.o values for HTS samples in which a plurality of samples are tested seriatim without the need for individual supervision.
Still another object of the present invention was to provide a machine for determining hysteresis curves and F.sub.o values for a plurality of HTS samples which can easily be adapted to continuous through semi-continuous modes of operation.
The invention consists of certain novel features and a combination of parts hereinafter fully described, illustrated in the accompanying drawings, and particularly pointed out in the appended claims, it being understood that various changes in the details may be made without departing from the spirit, or sacrificing any of the advantages of the present invention.